Stereophonic sound



Patented Jan. 23,i 1951 PTENT OFFICE Y s'rEnEornoNIc soUND Gilles Holst, Eindhoven, Netherlands, assignor to Hartford National Bank and Trust Company, Hartford, Ccnn.,as trustee Application March 25, 1947, Serial No. 737,010 In the Netherlands March 14, 1946 y Section 1, Public Law 690, August 8, 1946 Patent expires March 14, 1966 The invention relates to a method of successively scanning two or more oscillation records, for'example sound tracks, which are ar- Iranged in parallel relation on asingle carrier. Oscillation records as above referred to occur, for example, when stereophcnic records or pushpull records are made and, in general, when a plurality of oscillation tracks and, as the case lmay be, control tracks acting thereon are required to be reproduced simultaneously.

vThe method according to the invention is `characterized in that all the records are successively scanned at a high frequency rate and that the current pulses thus obtained which originate from each of the records, are combined to form a single signal and are pre-amplified, whereupon this signal is divided into its components in accordance with the number of records scanned. Thistime division may be effected in the manner known already from the multiplex telephony technique wherein a number of conversations are held through' one channel, for example by means of multivibrator circuits. Alternatively, use may be made of a multi-anode cathode ray beam tube the electron beam of which is caused to impinge, in synchronism with the scanning frequency, successively on the first, second and following anodes of the tube, the number of anodes depending on the number of tracks on the carrier signals, whereupon the individual components thus obtained are separately amplified and led to the respective reproducing devices.

By carrying out the method according to the invention, in addition to simplication, appreciable reduction of the number of devices required for reproduction is obtained since it is possible to utilise for all the records a common photocell and pre-amplier. Theseadvantages are greater according as the number of records on the carrier increases.

If, as is known in itself from French Patent Specication 885,556, use is made of the method lof high-frequency scanning in order to reproduce the records without any noise, for example .by means of a limiter, it is possible by carrying out vthe method according tothe invention to obtain, moreover, a saving in the number of limiters `since'in this case'for the'common signal a single limiter :may beutilized between the Acommon preamplifier and the device wherein thev signal is 50 divided into itsv components.

In one lpractical example .of carrying voutthe "method according to the invention,'scanning is effected by optical means.v To thatend a scan- -ning lightbeam is moved. at highfrequency in 6 anims( (ci. 17o-100.3)

a direction perpendicular to the direction vof travel of the carrier on which,` for example`,'a stereophonic double-track is provided. The beam of light modulated successively with very small 5 time intervals by each of the records falls on a single photocell. The current pulses thus combined to form one signal are pre-amplified and, as the case may be, deprived, in the manner 'known from the above-mentioned French pat- .10 ent specication, for example by means of a limiter, of the amplitude distortion which gives rise to the back-ground noise, whereupon this signal, according to the number of scanned records, is divided into the'two stereophonic comvponente.

In another example of carrying out the method according to the invention, an optical image -of the record, which, for example, may also be a stereophonic double-track, is formed on the image cathode of a so-called image dissector tube and the electrical image thus formed is scanned at a high frequency rate. The signal obtained is pre-amplified and then, in a similar manner as indicated above, divided again into the two kstereophonic components.

' The method according to the invention will be explained more fully with reference to the accompanying diagrammatic drawing which represents a few embodiments of the devices to be used. f

Fig. 1 represents a known device for jointly scanning by optical agency, for example, a stereophonic double-track.

y Fig. 2 represents a device for carrying out the 5 method according to the invention, wherein a stereophonic double-track is optically scanned at .high frequency.

Fig. 3 graphically represents the signal which has passed the pre-amplifier of Fig. 2.

,0 Fig. 4 shows the device for carrying out the method according to the invention wherein an lelectrical image of a stereophonic double-track is scanned.

The light emitted by a projection lamp I in 5 Fig. 1 .passes through a slit-shaped diaphragm 2 and-through a lens 3, resulting in thev production of a narrow beam of light v.which scans a stereophonic. double-track` 4 provided on a carrier -The light modulated by the records 4-is intercepted-by photocells 6v and transformed Yby the latter into electric-current variations which are `led-through separate-channels successively viapre-ampliersl and' final ampliers- 8 to 5s Referring to Fig. Zrthetwo stereophonic records 4 of the carrier 5 are successively scanned, in accordance with the invention, by a beam of light I moving at a high frequency rate. The light modulated by. the records 4 is intercepted by a single photocell ligand transformed'by the latter into electric current pulses, whereupon this signal is passed on to a common pre-amplifier 'I. The signal which has passed the pre-amplifier "I is represented in Fig. 3 wherein the voltage 4of this signal is plotted as a function of time for the case wherein scanning is effected `only in one direction perpendicular to the direction of travel of the records, as indicated in Fig. 2 for the sake of clearness by an arrow II.

The pulses I3, I3', I4, I4' etc. originating respectively from one of the two --stereophonic records 4, occur therein pair-Wise. It is `evident that the scanning may also take place in both directions perpendicular to the direction of travel of the records (see arrow I2), which results in "-thatthe-pulses I3, I3', I5, L5" etc. or'the pulses 14,5 I4" i6; I Bchange their places.

`Ifmperfection, soiling and `damage of the .carrier .material become Ymanifest by diminution fof 1.the intensity of the light falling upon the -photocell S owingto which variations in the am- ;plitudeoftthe block:signal are produced. The fwidthfoi :thezblock signal .depends on `the duration of each pulse and constitutes an index to the; amplitude tof Ythe oscillation to .be reproduced. 'lhe signal their passes through a limiter I'I which imay--be-of the type .described-ini the above-mentioned ,French patent specication owing to Awhichthe Vamplitude distortion arising from the background noise is eliminated since this device 'Eis onlyresponsive'to .the variations in width of :the'blocksignal withthe maximum amplitude :which is. represented by line A in Fig. 3.

Subsequently, thesignal is led to a cathode I8 cita device I9V in whicha multi-anode cathode ray `deflection beam tube is' combined with two amplifiers L-Ilrto form a single unit. The cathode activated iby the lpulses I3 and I3' etc, -emits velectrorns which are deflected, in synchronism with the scanning frequency., alternately to either lof-two anodes .2l of the device-L9, which anodes .are connectedto the respective input circuits of the ampliersl, the pulses I3, I4, I5, etc. and -.the:pulses I3', I4', I5', etc. of the common signal, originating from the two sterophonic tracks, .being thus separated. Subsequently they are stereophonically reproduced without anynoise by means of loudspeakerslz.

Upon comparison of Figures l and2 it will be .seenthat by carrying out the invention economy .in the number-of photocells land pre-amplifiers required for reproduction is obtained, which economyis greater according as the number of records provided ontheicarrier increases.

.Itmay also he seen. from Fig. 2, that a similar Veconomy may be obtained in the number of -llin'litersincomparison with the case wherein the two records are scanned each separately at high frequency.

In Fig. 4 an'image Aof stereophonic records 2,5 provided on acarrier "26 isthrown, by meansgof a 4 projectionlampg23 and lenses 24, on a photo- 'cathodeZ'I'of animage^tube 23. An example of this type Oitube may be found in the text Radio `Engineeringof Terman, 3rd Edition, page '830. The'electron beam emitted by the photovfcatlflodeZIis moved ata high frequency rate in ttheknown manner'over they opening of a collectfing screen-29. The-electrons which are allowed to pass fall on an anode 3G which 4is coupled with fthe inputccircuitof a ipreaampliiierl which is common to both records.- The signal thus obtained, which has a shape similar to that shown in Fig. 3, is led successively to an amplitude vlimiter 32and an amplifyingldeviceS as shown in'Eig 2 whereinthe signaliis -fdeprivedirom any noise and is divided into its composing components, the signal being subsequently stereophonically reproduced by means of the loud- Aspeakersyn.

Whatl claim is:

l. Instereophonic apparatus for the separate electrical reproduction of a plurality of light transmitting oscillation tracks of variable light permeability, thetracks lying in parallel relation along a carrier arranged for continuous movement, the ,combination comprising means to scan successively said tracks in a direction normal to the direction of carrier movement periodically at a'highfrequency to produce successive voltage pulses whose widths depend on the respective lighttransm-ission characteristics-oi said tracks, a

llike plurality :of electrical 'reproducing channels,

and .distributor means to apply :said pulses 4sequentially `to said .channels in .synchronism vwith the successive operation :of f said .scanning -means .2. in stereophcnicapparatus-for the separate :electrical Yreproduction of ,a plurality .of -light transmitting oscillation 'tracks oi variable light permeability, the tracks. lying 'rn parallel relation alonga. carrier arranged :for continuouszmovenient, "the ycombination .comprising nieansto iscan lsuccessively sai-:l tracks:v in a-directionfnormal to the. d

otion of carrier movement :periodically at a high frequency toxproducensuccessive voltage pulses Vwhose widths f depend on 'the-respective 'iight transmission characteristics of said tracks,

velectrical reproduction or" a plurality of light trans iitting cscillaticntracks of variable light ity, .the tracks lying in parallel relation yalong a carrier arranged 'for continuous movement, the combination comprisinga photoelectric device arranged to intercept light transmitted `through vsaid tracks, means to `succes- Hsively illuminate said tracks in a direction nor- "mal to the direction of carrier movement to produce successive Ycltage pulses in said device whose widths depend en the respective light transmission characteristics of said tracks, a like plurality of electrical reproducing channels, rand distributor means to apply the pulses developed by said Vdevice sequentially to said channels in `synchronism 4'with said scanning .means e. In stereophonic apparatus for the separate electrical reproduction or a plurality of light transmitting vsound tracks of variable light perfnieahility, the 'tracks lying in lparallel relation along Va carrier arranged `for continuous movement, the combinationcomprising -a photoelectric device arranged 'to Vintercept light transmitted through said tracks, means to successively illuminate said tracks ina direction lnormal to the direction of carrier-movement `to .produce ysuccessive voltage 4vpulses in said device whose widths depend on the respective lighttransmisasionrcharacteristics of. :saldi sound -tracks, a oathode-ray beam tube provided with a plurality of spaced anodes and deilection means, means to modulate the intensity of said beam with the successive pulses produced by said device, means to deect said beam in synchronism with said scanning operation to cause said beam to strike a respective anode in concurrence with the scanning of a respective track,and a plurality of sound reproducing channels each coupled to a respective anode to receive the pulses developed thereon.

5. ln stereophonic apparatus for the separate electrical reproduction of a plurality of light transmitting sound tracks of variable light permeability, the tracks lying in parallel relation along a carrier arranged for continuous movement, the combination comprising `a photoelectric device arranged to receive light through said tracks, means to successively illuminate said tracks in a direction normal to the direction of carrier movement to produce successive voltage pulses in said device whose widths depend on the respective light transmission characteristics of said sound tracks, a cathode ray beam tube provided with a plurality of spaced anodes and deection means, means to modulate the intensity of said beam with the successive pulses produced by said device, means to deflect said beam in synchronism with said scanning operation to cause said beam to strike a respective anode simultaneously with the scanning of a respective track, a plurality of sound reproducing channels each coupled to a respective anode to receive the pulses developed thereby, and an amplitude limiter interposed between said photoelectric device and said cathode ray tube whereby said tube is modulated by constant amplitude pulses of varying Width.

6. In stereophonic apparatus for the separate electrical reproduction of a plurality of light transmitting sound tracks of variable light per- 6 meability, the tracks lying in parallel relation along a carrier arranged for continuous movement, the combination comprising means to illuminate a narrow area of said tracks transverse to the direction of carrier movement, an image dissector tube having a photocathode, an output` electrode arranged to receive a cathode ray beam from said photocathode and means to deflect said beam across said output electrode, means to project a light image of said illuminated tracks on said photocathode, means to deflect said beam across said output electrode at a rapid rate 'to produce successive pulses at said output electrode whose widths depend on the respective light transmission characteristics of said tracks, a'fplurality of electrical reproducing channels, and distributor means to apply the pulses developed at said output electrode sequentially to said channels in synchronism with said deflection operation whereby the pulses derived from the respective tracks are applied to separate channels.V4

GILLES HOLST.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,191,565 Henroteau Feb. 27, 1940 2,195,676 McCarty Apr. 2, 1940 2,249,606 Frielus July 15, 1941l` 2,287,965 Borberg June 30, 1942`Y 2,303,456 Hardenberg Dec. 1, 1942 2,347,084 Cooney Apr. 18, 1944 2,352,696 DeBo'er et al July 4, 1944 2,367,277 Henroteau Jan. 16, 1945 2,414,666 Poulsen Jan. 21, 1947 2,415,981 Woli Feb. 18, 1947 

